This invention relates in general to vacuum apparatus for compacting, rigidizing and/or holding fabric and the like while being cut or otherwise worked and deals more particularly with improvements in bristle beds for vacuum tables. Heretofore vacuum tables have been available which include beds of penetrable bristles which define generally horizontally disposed work surfaces for supporting material to be held firmly in place by vacuum. Such apparatus is disclosed in U.S. Pat. No. 3,765,289 to Gerber et al, issued Jan. 15, 1971 and assigned to the assignee of the present invention. A typical apparatus of this type includes a bristle bed formed from a plurality of bristle blocks. Each block has a gas impermeable base portion and a gas permeable body portion defined by a multiplicity of bristles which project from the base portion. One or more vacuum channels which communicate with a vacuum chamber are arranged along one or more sides of the bed in communication with the gas permeable body portions of the bristle blocks above the bases of the blocks to induce airflow from the bed in transverse directions relative to the bristles and toward the vacuum channels. In such a vacuum apparatus for a cloth cutting machine or the like, it is generally desirable that the bristle bed have a high bristle density to reduce lateral bristle deflection which causes valleys to occur between the bristles and into which sheet material supported on the vacuum table may be drawn. However, high bristle density tends to restrict transverse airflow through the bristle bed and toward the laterally disposed vacuum channels. Air which enters the cut formed in the sheet material supported on the bristle bed must flow through the relatively dense bed of bristles to the vacuum channels if holding pressure is to be maintained in the vicinity of the cut. If such a vacuum table installation has a relatively wide bed, vacuum channels may be provided at laterally opposite edges of the bed to reduce the length of the airflow paths from the central regions of the bed whereby to increase vacuum holding efficiency in central regions of the table. However, some holding efficiency is lost due to the relatively long airflow paths through the dense bed of bristles.
It is the general aim of the present invention to provide an improved bristle bed for a vacuum table wherein the length of airflow paths through the bed is minimized for increased compacting, rigidizing and holding efficiency. A further aim of the invention is to provide an improved durable bristle bed for low cost manufacture and which may be economically repaired or replaced.